Document unsupported types (#30344)
Summary:
This adds a listing of the parts of the `typing` module that are unsupported
This is also a first pass decisions on features are 'unlikely to be implemented' vs 'not implemented' so they're open to discussion
](https://our.intern.facebook.com/intern/diff/18665628/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/30344
Pulled By: driazati
Differential Revision: D18665628
fbshipit-source-id: 22b8ebbde23df03839306cdb4344ca18a44f2c29
